Abstract

Members of the diatom family Rhopalodiaceae possess cyanobacteria-derived intracellular structures called spheroid bodies (SBs) that very likely carry out nitrogen fixation. Due to the shortage of molecular data from SBs and rhopalodiacean diatoms, it remains unclear how SBs were established and spread in rhopalodiacean diatoms. We here amplified the small subunit ribosomal DNA sequences from both host and SB in three rhopalodiacean diatom species, Epithemia turgida, E. sorex, and Rhopalodia gibba. Phylogenetic analyses considering these new sequences clearly indicate that the SBs were acquired by a common ancestor of rhopalodiacean diatoms and have been retained during host speciation.

Keywords

Nitrogen fixation Endosymbiosis Organelle Cyanobacteria Diatoms

Takuro Nakayama and Y. Ikegami contributed equally to this study.

Electronic supplementary material

The online version of this article (doi:10.1007/s10265-010-0355-0) contains supplementary material, which is available to authorized users.

Notes

Acknowledgments

We would like to thank Haruka Kogure and Yoshihisa Hirakawa (University of Tsukuba) for kindly providing a sample of Saiko and valuable help with laboratory works, respectively. Takuro Nakayama is supported by a JSPS Research Fellowship for Young Scientists (DC1). YI is supported by a grant from JSPS (no. 21370031).